Eta Horologii

Eta Horologii (η Horologii, η Hor) is a binary star system[3] in the southern constellation of Horologium. It is visible to the naked eye with a combined apparent visual magnitude of 5.31.[2] Based upon an annual parallax shift of 21.95 mas as seen from Earth,[1] it is located around 149 light years from the Sun.

Eta Horologii
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Horologium
Right ascension  02h 37m 24.37297s[1]
Declination −52° 32′ 35.0855″[1]
Apparent magnitude (V) 5.31[2]
Characteristics
Spectral type A6 V + F0 V[3]
B−V color index +0.27[2]
Astrometry
Radial velocity (Rv)−3.0±7.4[4] km/s
Proper motion (μ) RA: +112.70[1] mas/yr
Dec.: +3.73[1] mas/yr
Parallax (π)21.95 ± 1.10[1] mas
Distance149 ± 7 ly
(46 ± 2 pc)
Absolute magnitude (MV)2.13[5]
Orbit[6]
Period (P)3.01±0.18 yr
Semi-major axis (a)0.0231±0.0014″
Eccentricity (e)0.16±0.14
Details
η Hor A
Mass1.56[7] M☉
Luminosity12.6[8] L☉
Surface gravity (log g)4.21[7] cgs
Temperature7,552±257[7] K
Rotational velocity (v sin i)6.6±2.2[5] km/s
Age474[7] Myr
Other designations
η Hor, CPD−53° 457, FK5 2182, HD 16555, HIP 12225, HR 778, SAO 232835[9]
Database references
SIMBADdata

The orbit for this pair is not yet well constrained. They appear to have an orbital period of three years and an eccentricity of roughly 0.16.[6] As of 2012, the pair have an angular separation of 78.7 mas, which corresponds to a projected separation of 3.6 AU.[3] The primary member, component A, is an A-type main sequence star with a stellar classification of A6 V. The secondary, component B, has an inferred class of F0 V, which would indicate it is an F-type main sequence star.[3]

References
  1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J.
  3. Marion, L.; et al. (October 2014), "Searching for faint companions with VLTI/PIONIER. II. 92 main sequence stars from the Exozodi survey", Astronomy & Astrophysics, 570: 12, arXiv:1409.6105, Bibcode:2014A&A...570A.127M, doi:10.1051/0004-6361/201424780, A127.
  4. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, A61.
  5. Ammler-von Eiff, M.; Reiners, A. (2012), "New measurements of rotation and differential rotation in A-F stars: Are there two populations of differentially rotating stars?", Astronomy & Astrophysics, 542: A116, arXiv:1204.2459, Bibcode:2012A&A...542A.116A, doi:10.1051/0004-6361/201118724.
  6. Malkov, O. Yu.; et al. (2012), "Dynamical Masses of a Selected Sample of Orbital Binaries", Astronomy & Astrophysics, 546: 5, Bibcode:2012A&A...546A..69M, doi:10.1051/0004-6361/201219774, A69.
  7. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146.
  8. McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x
  9. "eta Hor -- Double or multiple star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-04-25.
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